The invention relates generally to the field of wind power generation, and more particularly to techniques for regulating power rating of wind turbine generators.
Wind turbine generators are regarded as environmentally friendly and relatively inexpensive alternative sources of energy that utilize wind energy to produce electrical power. A wind turbine generator generally includes a wind rotor having a plurality of blades that transform wind energy into rotational motion of a drive shaft, which in turn is utilized to drive a rotor of an electrical generator to produce electrical power. Modern wind power generation systems typically take the form of a wind farm having multiple such wind turbine generators that are operable to supply power to a transmission system providing power to a utility grid.
Wind is an intermittent resource and collective power output of the wind farm is significantly influenced by changes in wind conditions. Wind conditions may change drastically in a relatively shorter time span. Generally, power output of a wind turbine generator increases with wind speed, until the wind speed reaches the rated wind speed for the turbine. With further increases in wind speed, the turbine operates at rated power up to a cut off value or a trip level. This is generally the wind speed at which dynamic loads on the wind turbine cause the mechanical components of the turbine to reach a fatigue limit that tend to shorten the lifespan of the turbine. As a protective function, at wind speeds higher than a certain speed, wind turbines are often required to shut down, or reduce loads by regulating the pitch of the blades or braking the rotor, thereby leading to a reduced power output of the wind turbine generator, and consequently of the wind farm. However, this limits the maximum power capture to the rated power set point, and increases the effective cost of energy of the wind farm. Thus, for a wind turbine generator, there exists an inherent trade off between the power at which it operates and its life, as protected by reference to the fatigue limit and other factors, that is, the maximum output rating.
Additionally, mechanical and thermal loads are the major factors that determine the rating of a wind turbine generator. The maximum power output of a wind turbine generator is decided at the design stage and is used to select appropriate ratings for other key components such as electrical generators, transformers, power conversion equipments, bearings, shafts, gearboxes, and so forth, with certain conservative assumptions. Conservative design practices and flat ratings of these components do not allow the operator to harness the excess energy in the wind once the full rated output has been achieved even if there may be additional energy in the wind. Hence, current techniques have limitations for achieving high power output during high wind speed conditions.
It is therefore desirable to provide a technique to efficiently and cost effectively harness higher wind energy during high wind speed conditions while ensuring baseline life of the wind turbine generators. It is also desirable to improve the design of the wind turbine generators so as to harness higher wind energy than that possible by the current designs.